1. Field of Invention
This invention relates to polyester resins which have been modified with siloxane block polymers to obtain copolymers with discrete silicone blocks. The resulting silicone-modified polyester resins maintain the physical properties of a polyester resin and yet subsequent processing exhibits the surface properties of a silicone sheathed material. The invention also relates to fibers made from the silicone-modifed polyester resin and their use in a variety of products.
2. Prior Art
Polyesters have been characterized as heterochain macromolecular compounds that possess a plurality of carboxylate ester groups as components of their skeletal structure as distinguished from other ester-containing polymers, such as cellulose esters, poly(acrylates) and poly(vinyl esters) which have carboxylate groups forming part of pendants from the skeletal structure. Polyesters have found wide utility, being used as fibers, films, plasticizers and polyurethane intermediates to name but a few applications.
Although many reactions are possible for the synthesis of polyesters, conventionally the polyesterification of dicarboxylic acids or their functional derivatives with diols followed by a polycondensation reaction is most widely utilized.
Despite being suitable for many applications, polyesters have been treated with a variety of additives to enhance their physical properties. Silicone has found many uses in conjunction with polyesters, including hydrolytic stability, lubricity, water repellancy and the like. Traditionally, these silicones were applied topically to the finished polyester, see for instance U.S. Pat. No. 4,105,567. However, there has continually been an effort to modify the polyester resin itself in such a way as to provide the polyester resin with the properties of the silicone without adversely affecting its physical characteristics.
An early attempt at such a modification was U.S. Pat. No. 3,296,190 where polyesters were modified with a carbodiimide and a silicone in an effort to stabilize the ester groups from hydrolysis.
Shortly thereafter, two related patents by Union Carbide Corporation, U.S. Pat. Nos. 3,579,607 and 3,701,815, sought to modify the polyester with silicone blocks. This work, as it relates to fibers, suffered from two drawbacks, nitrogen contained in the siloxane blocks was released during copolymerization and discolored the resulting polyester resin and the large amount of silicone employed adversely affected the ability to process fibers.
Polyethylene terephthalate was reported as one of the polymeric materials that could be modified by dispersing polysiloxanes containing polymerized vinyl units, such as styrene, in the preformed organic polymer in U.S. Pat. No. 3,691,257. This patent noted that surface modification of the polymeric material is obtainable and more permanent in nature over topical treatments or simple mixtures when the polymeric material is chemically modified with polysiloxanes.
In U.S. Pat. Nos. 3,674,724 and 3,749,757 polyesters for reinforced elastomers were manufactured by reacting a polycarboxylic acid and a polyol with either an organosilane or a polysiloxane. The silicone-containing material was utilized to provide additional sites for crosslinking the polymeric material to obtain improved tensile strengths under high load.
Acrylic and methacrylic esters were modified with polysiloxanes in U.S. Pat. No. 4,153,640 to obtain modified polymers suitable for treating fibrous materials, including textiles, in an attempt to offer the advantage of water repellancy.
Most recently, a team of scientists at Goodyear Tire and Rubber Company have explored silicone-modification of polyester films as a means to improve the slip characteristics of such films, see U.S. Pat. Nos. 4,348,510, 4,452,962 and 4,496,704. These films are designed to exhibit improved optical clarity for use in visual applications. Here, the silicon atom distribution is inhomogeneous (i.e., there will be local concentrations of dimethylsiloxy mers) while the silicone block distribution is random and hence homogeneous. This type of incorporation will not favor migration of the silicone domains to the surface and can be expected to alter the bulk physical properties of the polyester resin so formed.
Despite numerous references to silicone-containing materials being utilized to modify polyesters in an effort to realize the characteristics obtainable when these same polyesters are treated topically with silicone-containing materials, there continues to be a need for a modified polyester having these attributes which does not suffer from a reduction in its physical properties as a result of incorporating blocks of silicone-containing material into the skeletal structure.